1. Field of the Invention
The present invention relates to a thermal processing apparatus that performs thermal processing of a semiconductor wafer and a glass substrate, etc. (hereinafter referred to simply as a “substrate”) by irradiating light to the substrate, as well as a method of adjusting irradiation intensity thereof.
2. Description of the Background Art
In an ion activation step of a semiconductor wafer after being subjected to ion implantation, there has heretofore been used a thermal processing apparatus such as a lamp annealing apparatus using halogen lamps. In such a thermal processing apparatus, the ion activation of a semiconductor wafer is carried out by heating (annealing) the semiconductor wafer to temperatures of, for example, approximately 1000° C. to 1100° C. This thermal processing apparatus is constructed so as to elevate the temperature of the substrate at a speed of about several hundreds of degrees per second, by utilizing the energy of light irradiated from the halogen lamps.
The above-mentioned thermal processing apparatus is usually provided with a plurality of lamps and a mechanism for measuring wafer temperatures during processing and performing feedback control of the output to the lamps on the basis of the measurements results. For example, Japanese Patent Application Laid-Open No. 2001-244212 discloses a technique of dividing a plurality of halogen lamps into several zones and performing feedback control of the power of the halogen lamps per zone.
On the other hand, even when the ion activation of a semiconductor wafer is executed with a thermal processing apparatus that elevates the temperature of the semiconductor wafer by halogen lamps at a speed of about several hundreds of degrees per second, the profile of ions implanted into the semiconductor wafer becomes round. That is, it has been found to cause the phenomenon that ions diffuse by heat. In case that this phenomenon occurs, even if ions are implanted at a high concentration into the semiconductor wafer surface, the implanted ions may diffuse. This introduces the problem that it is necessary to implant more ions than necessary.
In order to solve the above problem, for example, Japanese Patent Application Laid-Open Nos. 59-169125 and 63-166219 have proposed such a technique that only the temperature of the surface of a semiconductor wafer after being subjected to ion implantation is elevated in an extremely short period of time (not exceeding several milliseconds) by irradiating flashlight to the surface of the semiconductor wafer by use of xenon flash lamps, etc. For the temperature elevation in a very short time by the xenon flash lamps, the ions will not have a sufficient time to diffuse. Therefore only the ion activation is executable without rounding the profile of ions implanted into the wafer.
A thermal processing apparatus using xenon flash lamps is also provided with a plurality of flash lamps. These flash lamps have an individual difference due to manufacturing error, circuit characteristic error, secular change and the like. Such an individual difference might cause ununiform irradiation intensity, and the output of respective flash lamps needs to be adjusted. However, for flash lamps of which irradiation time is extremely short, it is impossible to perform feedback control of the lamp output on the basis of the measurements results of the temperatures of the semiconductor wafer. This requires that the characteristic of a semiconductor wafer after being subjected to the actual thermal processing be measured and the output of the respective flash lamps be adjusted based on the measurement result.
Unfortunately, it is a considerable increase in cost and hence unrealistic that the voltage at both terminals of the respective flash lamps are adjusted per flash lamp by making changes in the power supply circuit of the flash lamps.